1. Field of the Invention
The present invention relates to stretch-blow-molded polyester containers that are opaque. In particular, the present invention relates to stretch-blow-molded opaque polyester containers that have superior barrier properties for oxygen, carbon dioxide, and visible light. More specifically, the present invention is designed to be opaque such that less than 15% transmission of visible light (500 nm) passes through a 0.4-millimeter sheet of container material. The opacifying material may be any material compatible with polyester resin. Generally, the finer the powder, the better the opacifying properties. Selection of certain opacifying materials can also result in favorable reheat properties, gas permeation—barrier improvements, and when the resin contains both opacifying material and oxygen scavenger there can be a synergistic effect with respect to CO2 permeation.
2. Prior Art
Current stretch-blow-molded polyester containers are transparent. The industry demands transparent polyester containers because the consuming public strongly prefers to see all food items. When the polyester containers are employed as food grade containers for such things as beer, soft drinks, bottled water, baby food, catsup, mustard and mayonnaise containers, etc. it is psychological that the consuming public must see the food. This burden places many restrictions on the container. For example, when looking for a suitable barrier material as an additive for the polyester container, or an acetaldehyde or oxygen scavenging compound, for example, it is necessary to find compounds that do not cause haziness or discolor the clear bottle. Consequently, much research and development has gone into finding suitable barrier materials and scavenger materials which maintain the polyester container transparent.
U.S. Pat. No. 4,427,122 to Jakobsen discloses a dual layer coextruded blank in which one layer contains a pulverulent material that is impermeable to light or comparable radiation. This material may, for example, consist of a metal, for example aluminum powder. The blank is then blow-molded into a bottle using conventional techniques.
British Pat. 2,299,965 to McRoberts et al discloses the addition of particles to polyester resins used to make a bottle to present a different visual appearance, i.e. a “flitter” to give a sparkling effect. The aesthetically pleasing appearance means that the particles are easily visible to the naked eye. The bottle may be colored. Moreover the particles must be very shiny and reflective to give the sparkling effect.
U.S. Pat. No. 3,371,062 to Curry discloses the addition of aluminum powder into polypropylene to resist ultra violet and oxidative degradation. The resin was employed for making pipe, rope, or fiber. There is no mention of a bottle, not even a stretch-blow-molded bottle.
U.S. Pat. No. 4,772,656 to Tanner discloses the incorporation of aluminum powder in polyolefins to improve the barrier properties to the permeation of fluid hydrocarbons through the molded container walls. Containers for hydrocarbon fluids are usually injection molded. Tanner does not mention stretch-blow-molding.
U.S. Pat. No. 5,258,233 to Mills et al discloses the use of TiO2 in thermoformed or injection molded trays as a colorant to improve the opaque whiteness of a blend of polyamide and a nucleating agent in a crystallized polyester film. This reference also discloses the importance of employing a clear, colorless resin for use in stretch-blow-molded bottles.
U.S. Pat. No. 5,021,515 to Cochran et al discloses the use of partially aromatic polyamide as an oxygen scavenger when used in a concentration of from about 4 to about 6% by wt., based on the weight of the resin.
There is a need in the industry to improve uniform, single layer stretch-blow-molded polyester containers that allow cost effective solutions for barrier materials, scavenger compounds, and more effect production processes that are substantially less burdensome than those process conditions necessary to keep a polyester container transparent. In none of the discussed patents is there a teaching to the use of opacifying materials in stretch-blow-molded polyester containers to mask the color formed by specific additives that are used in transparent containers for food packaging.
The present invention is an approach diametrically opposed to stretch-blow-molded polyester transparent containers that until now have always required clear, colorless containers.